Ah, I didn't know drg also had a skill that slowed down enmity gain. Also I think most fights show where it's coming from.. take T4's soldiers and knights for example, if your melee is really slow on knights while your mages are burning through their soldiers like nothing... well... you can almost spot the problem right there.
I'm not gonna say that there aren't times where one add is killed right when bugs pop with dread and the dread still goes down fine but when the bugs spawn the add should definitely be close to dead if not dead already, in this situation theres normally buffs that can help killing the dread too so it goes by fine with the right dps.
But why would you need a parser to tell you that you're gonna die from slow melee or magical dmg? you should be able to plainly see that much. In those situations it's just really plain to see.
(T1 can be done even with some in DL, I won't go into details about that turn considering when knowing what to do it's normally done smoothly and T2 is just enraged now. T5 well... I don't think people with serious dmg issues would have the easiest time in T4 so... I won't mention T5 due to that and... tbh Idk much about T5 to talk on it.)
Putting coil aside, Dungeons.... most are a cake walk, (they just take learning) so you shouldn't need to watch someone else's dmg to see if they can get through those.
Lastly EX's, Yeah a parser may be explained as helpful in those but sometimes the person messing up dies first or is noticed by someone else... so it doesn't matter anyways, most seeing "baddies" (as some call people) are catch them and insta kick them whether they were just going to learn or not.
Least thats what I've seen done in some pfs on our server anyways, so a parser would probably just be used to harrass in that situation more than anything. (If just dmg is the issue and no one is dying then normally asking for people to bum it up or making suggestions does help least in runs I've had.)
Again just my view, I am not saying I am 100% right or anything. I play a certain way and I'd not use a parser myself. I don't expect my views or feelings to change if someone can or will use one themselves nor if they find them useful.